Temperature controlled and adjustable specimen stage for scientific instruments



March 2, 1965 A. J. CARDILE 3,171,955 TEMPERATURE coNTRoLLED AND ADJUSTABLE SPECIMEN STAGE FOR SCIENTIFIC INSTRUMENTS 4 Sheets-Sheet 1 Filed March 30, 1962 QNH Sw @Qi \K EQ. um m A E @EESW W L E@ SE Q 7 March 2, 1965 A. J. CARDILE 3,171,955 TEMPERATURE NTROLLED AND ADJUSTABLE SPECIMEN STAG OR SCIENTIFIC INSTRUMENTS Filed March 30, 1962 4 Sheets-Sheet 2 mp .m m f Wr 1J. m W 4 A. J. CARDILE 3,171,955 NTROLLED AN DJUSTABLE SPECIMEN oR SCTENTTF INSTRUMENTS March 2, 1965 TEMPERATURE co STAGE F 4 Sheets-Sheet 4 Filed March 50, 1962 INVENTOR. f/vafzaJhia/f States `Patent v. 3,171,955 TEMPERATURE CGNTROLLED' ANI) ADJUST- ABLE SPECIMEN STAGE FR SCIENTIFIC INSTRUMENTS Y Angelo J. Cardie, Haddontield, NJ., assigner to Radio Corporation of America, a corporation of Delaware Filed Mar. 30, 1962, Ser. No. H3326 13 Claims. (Cl. Z50-495) This invention relates to instruments for the examination of microstructure, and more particularly to electron microscopy.

The invention deals with the establishment of the environment of a specimen under examination and is generally useful in any scientific instrument which handles specimens. The invention is especially suitable for use in an improved specimen stage for an electron microscope wherein the temperature in the vicinity of the specimen may be varied over a wide range of temperatures.

Recent advances in technology have brought about the need for more data as to the microstructure of physical and biological speciments at temperatures far removed from ambient temperatures. Means for refrigerating specimens to temperatures which range from ambient temperatures to very low temperatures, say around 200 C., are provided in accordance with this invention.

The electron microscope has long been used for the examination of and for obtaining data on microstructures. However, the conditions of high vacuum within the electron microscope column and the sensitivity of 'the microscope to changes in its physical dimensions and to specimen excursions which might be thermally induced have heretofore prevented the successful introduction of means for changing the temperature environment of a specimen undergoing electron miscroscope examination over the desired temperature range.

Some of the problems which are encountered in attempting to operate an electron miscroscope specimen stage at temperatures far removed from ambient temperatures are the following:

(l) Dimensional changes which produce aberration in the image produced by the microscope.

(2) Significant thermally induced excursions of the specimen during examination, and particularly during the taking of photomicrographs.

(3) Image deterioration and loss of resolving power because of disposition of magnetic and electric field producing and distorting elements in 'the vicinity of the electron beam.

(4) Deterioration of the vacuum in the microscope column due to the introduction of a refrigerant and a concomitant increased contamination in the column.

(5) Vibration of the specimen due 'to percolation of a iiuid refrigerant.

(6) Miniaturization of specimen refrigeration units so that they may occupy the space allotted in the microscope for the specimen stage.

A specimen stage has been proposed which substantially solves the problems mentioned above and permits a specimen to be refrigerated to very low temperatures in the range of the temperature of liquid nitrogen (around -200 C.). This stage includes a support for receiving a specimen holder and a refrigeratory body in the form of a receptacle for containing a liquid refrigerant. The refrigerant receptacle and the support have fin-like members extending therefrom which are interleaved in radiative heat exchange relationship. It is sometimes desirable to provide more rapid cooling of the specimen than is brought about by radiation alone.

Accordingly, it is an object of this invention to provide a specimen stage, especially adapted for use in an lCe electron microscope, for refrigerating a specimen to very low temperatures at a rapid rate.

It is a still further object of the present invention to provide a specimen stage for a scientific instrument, such as an electron microscope, wherein a specimen may be rapidly cooled to a very low temperature through the removal of heat therefrom either by conduction or by radiation.

It is a still further object of the present invention to provide an improved specimen stage for an electron microscope wherein a specimen may be refrigerated to very low temperatures and which also provides for a more perfeet vacuum than would be available without the use thereof.

It is a still further object of the present invention to provide an improved specimen stage for an electron microscope which includes devices for altering the temperature of the specimen without introducing heavy mechanical loads on mechanical drives for orienting the stage.

It is a still further object of the present invention to provide an improved specimen stage for an electron microscope having improved mechanism for orienting the stage, which mechanism is more immune to unwanted movements of the specimen stage than stage mechanisms which have been available heretofore.

Briefly described, a specimen stage for refrigerating a specimen which embodies the invention may include a refrigeratory body, such as a refrigerant receptacle, and a specimen mounting. A heat exchanger in the form of interleaved, fin-like elements extending Separately from the specimen mounting and from the refrigerant receptacle is also provided. The tins of the heat exchanger may be separated from each other to provide radiative heat exchange relationship between the specimen mounting and the refrigerant receptacle. Means are provided in the stage for establishing a temporary thermal conduction path between the refrigerant receptacle and the specimen mounting, whereby the specimen can be cooled by conduction. These means may, for example, involve a movable mounting for the refrigerant receptacle and its heat exchange iins. A mechanism coupled to the refrigerant receptacle is provided for shifting the receptacle so as to establish a thermal conducting path therebetween, as by way of their heat exchange tins, for example. The specimen may be examined by the usual electron microscope techniques after being subjected to conductive coolingand while being subjected to radiative cooling.

The invention itself, both as to its organization and method of operation, as well as additional objects and advantages thereof, will become more readily apparent from a reading of the following description in connection with the accompanying drawings, in which:

FIG. l is a View partly in longitudinal section and partly diagrammatic schematically showing an electron microscope incorporating a specimen stage;

FIG. 2 is an enlarged plan view, partly in section, of the specimen stage of FIG. 1;

FIG. 3 is a sectional view taken along the line 3-3 of FIG. 2 and viewed in the direction of the appended arrows;

FIG. 4 is a sectional view taken along the line 4-4 of FIG. 3 and viewed in the direction of the appended arrows, showing particularly the mechanism for orienting the stage shown in FIG. 2;

FIG. 5 is a somewhat enlarged, fragmentary, sectional view taken along the line 5 5 of FIG. 4 and viewed in the direction of the appended arrows, showing portions of the mechanism of FIG. 4;

FIG. 6 is a sectional view of a specimen holder which also functions as a temperature measuring device;

FIG. 7 is a sectional View taken along the line 7-7 3 of FIG. 6 and viewed in the direction of the appended arrows; and

FIG. 8 is a schematic diagram ofthe electrical system associated with the temperature measuring device of FIG. 6.

General Referring more particularly to FIG. 1, there is shown an evacuable'housing 10 of an electron microscope .12. The housingmay be evacuated by a vvacuum pumping system 1 4. The microscope 12in`cludes a source of illumination 16 provided by an incandescent lament ,18, a cathode 20 and an anode 22. The lament 18 is Venergized and a difference of potentialwhich may, for example, be onehundred kilovolts between the cathode 20 and the anode 22 is provided by 'anoperating voltage supply 24.A The source of illumination 16..projects a beam of electrons, shown by the dash lineV 26, through a condenser lens 2 8, a specimen stage 30, an objective lens 32, an intermediate lens 34 and a projection lens 35 upon ailuorescent viewing screen 38. A photographic system 40 is disposed below the viewing screen 38 ,for the purpose of taking photomicrographs ,of animage of the specimen. The viewing screen is shifted out of the way ofthe photographic system when vphotomicrographs are to be taken. The lenses 28, 32, 3ftand` 36 are operated by current fromdiierent lens supplies 42, 44, 46 and 48, respectively. Thesesupplies include sources of direct current and electrical control equipment, such as potentiometers, which provide current for energizing the various lenses. The electron microscope 12 so far described is similar to the type EMU-3 electron microscope which is manufactured and sold by Radio 'Corporation of America, Broadcast and Communications Division, Camden 2, New Jersey, and is described in an instruction book issuedin 1957 byRadio Corporation of America, as Instruction Book 113-39031-3 (1960),

. The specimen stage includes a specimen holder 5) which is mounted on a vvmovable plate 52 supported on the spool ofthe objective lens 32. The specimen stage 30 also includes Ameans forrefrigerating the specimen contained in the kholder 50 to very lovfvl temperatures in the range of the temperature of liquid riitogen. -.195.8 C.). The refrigerating means includes a refrigeator`y body. By arefrigeratory body is meant an element which is adapted to maintaina temperature well below the ambient temperature. Innthe illustratedk apparatus, the refrigeratory body is provided by a receptacle 54 for containing liquid nitrogen and through which the liquid nitrogen may be kcirculated from an inlet port 56 toan outlet port 58. The inlet port 56 maybe coupled through a valve 60 to a source of liquid nitrogen, which may be, for example, a tank of liquid nitrogen containedin a Dewar flask orsimilar insulating container. nitrogen kmay also kbe introduced into the y,receptacle Aby pouring it into the inlet port 56. TheV outlet port may be coupled through a valve.6 2 to another container for recieving the liquid nitrogen. The valveA 62 may be left open to air for nitrogen to4 escape as.it..boils away in the receptacle 54. By selectively controlling the valves 60 and 62, the liquid nitrog'emmay. be introduced into, exhausted from, or circulated through the receptacle 54. Alternatively, the valves 60 and 62 maybe left` open.

Liquid nitrogen may be introduced by pouring a ,steady trickle there'of to maintain a certain 'level in the receptacle 54. Y

A heat exchanger 64 is Vprovided in the form of a iirst set of tins extending in one direction from the specimen holder 50 and a second set of ns extending in the opposite direction from the receptacle 54these 'two setsof tins being interleaved with each other in heat exchange relationship. This heat exchanger 64 provides thermal coupling between the specimen andthe refrigeratory body such that the'specimen is cooled almost4 to liquid nitrogen temperature. The heat exchanger 64 is shown with the The liquidV fins spaced from each other so as to provide for radiative heat exchange between the refrigerant receptacle 54 and the specimen holder 50. However, as will be explained hereinafter, the receptacle and its associated tins may be moved relative to the specimen holder so that there will be conductive, metal-tofmetal, thermal coupling between the specimen holder and the receptacle. When the specimen and the holder are coupled ink conductive heat exchange relationship, the specimen may be cooled much more rapidly than when the heat exchanger provides coupling radiation alone. l

Alternatively, the specimen holder and the refrigeratory body may be coupled in conductive heat exchange relationship lby introducing a dry gas `of high conductivity, such as hydrogen or helium, into the specimen `oharnbe' r The gas then conducts the heat betweentheinterleaved tins of the heat exchanger and causes the specimen to lcool very rapidly. It will be noted that the area of conduction between the tins is verylarge, while the path therebetween is short. Accordingly, even lthough the amount of heavy gas in the stage is small, rapid cooling ('for example, cooling to about liquid nitrogen .temperature in about 15 minutes) may be accomplished through the use of the heaviergas..

Several advantages tlow from the use of van arrangement of refrigerant receptacle specimen mounting and iin-type heat exchanger such as described above., These advantageswill be brought yout more fully hereinafter. A few of these advantages are briefly mentioned at this point as follows:

(l) Since the mechanisms for orienting the specimen holder are mechanically independent of the refrigeration apparatus, separation of the mechanical and thermal functions ofthe specimen stage is provided.

(2) The specimen holder 50 may be isolated from thermal conduction with any part of the microscope casing or column. This eliminates any unwanted heat s'inksor losses ,and Vaffords highly efficient radiative heat transfer. The specimen holderandheat exchangermay be fabricated as a unit and placed on, the movabl e plate 5 2 when examination of the micro-structure o f refrigerated spec'imen's is desired. Thus, the refrigeratedstage may be used as afi accessory whenever desired by the microscope user.

(3) The cold refrigerant receptacle acts as a Cold trap which makes the vacuum more perfect by trapping free molecules within the microscope columni Objective lens sectorl Referring, now, to FIGS. 2 land 3, there is shown a portion ofthe evacuablehousing 10 for the microscope column. The column itself is cylindrical in shape and is made up of thelens sectionsandother parts, Vacuum seals or gaskets are interposed between juxtaposed sections and partsin amannerknown in the microscope art. Oneofthese seals, an O -ring 66, is shown in FIG. 3 This O-ring 66 is disposed between a ring 68 lof magnetic material (iron, for example) Aand the upper Vflange 70 of thel spool 72 of l the objective lens '32. 1 'lhering :68 is secured to its immediately subjacent column member by means vof a plurality of screws '74, one of which 'is shown in FIG. 3.

YThe coil 76 ofthe objective lens 32 is wound around the spool72 between'the flange' 70 and another flange (not shown). One of the objectivelens polepieces 78 is mounted within the spool '72. A ring 80 of nonmagnetic material, such as brass, forms part of the hub of the spool 72. Another, upper pole piece i82 ofthe objective lens is mounted adjacent the upper `flange 70 of the spool. The pole pieces 78 and 8 2 have apertures 84 and 86, respectively. The polel pieces78 and 82 are spaced from each other by a cylindrical tube 88 loffnonm magnetic material, such as brass, which, with the ring 80, causes the magnetic ilux to pass between the p olepieces. A sleeve 90 of magnetic material, vsuch as iron, encom- `magnetic circuit of the lens for efficient lens operation.

Specimen stage The part 11 of the housing 10 which contains the specimen stage 30 is bell shape in plan, as shown in FIG. 2. The front of the housing part 11 is sealed by a door 13 which is removably held in place by thumb screws 15, one of which is shown in FIG. 2. A vacuum seal in the form of an O-ring 17 is disposed in a slot on the inner face of the door 13.

Another door 19 is located in the rear of the specimen stage housing part 11, which may be vacuum sealed in a manner similar to that of the door 13. This rear door 19 provides access to the specimen stage for cleaning a curved baffle plate 214, which functions as a cold trap type of vacuum pump, as will be more fully explained hereinafter.

The upper flange 70 `of the objective lens spool '72 (FIG. 3) provides a base or floor on which the specimen stage 30 of the microscope is mounted. Access to the specimen stage is through the door 13 (FIG. 2). When the door is closed, the column may be evacuated by the vacuum pumping system 14 (FIG. 1).

Specimen stage orienting mechanism The specimen stage 30 (FIG. 3) includes a plate or disc 92, preferably of a low expansion nickel steel, such as Invar. The disc 92 has a conically, downwardly, inwardly tapering opening 94 through the center thereof. This opening provides a socket in which the mounting for the specimen is removably received. Interior sectors of the disc 92 may be cut away, leaving the disc 92 in the form of a lightweight spider.

The disc 92 is movably mounted on three ball bearings 96. These bearings may be spaced circumferentially at convenient angles with respect to the axis of the disc 92. Two of these bearings 96 are shown in FIG. 3. The ball bearings 96 are held in recesses in the bottom of the disc 92 and ride upon inserts 98 of hardened steel in the upper flange 70 of the spool 72. The disc 92 is held down in position by three flat, wide hold-down springs 100, one of which is shown in FIG. 3. These hold-down springs are anchored in cantilever fashion by screws on a shoulder 102 on the upper flange 70 of the objective lens spool '72. The three springs 100 are spaced equidistantly from each other circumferentially around the disc 92, each one being anchored to the shoulder 102 in the manner described above. The springs 100 bear down on ball bearings 104 which are disposed in recesses in the top surface of the disc 92 and ride on hardened inserts 106 in the disc 92 (FIG. 3). The disposition of the bearings 104 is shown in FIG. 4.

The mechanism for orienting the plate or disc 92 is shown in FIGS. 3, 4 and 5. This mechanism includes a pair of screw-feed drives 108 and 109 (FIG. 4) and two backlash eliminating, leaf-type springs 110 and 112 which cooperate, respectively, with the drive mechanisms 108 and 109. The leaf springs 110 and 112 are held in position by means of clamping blocks 114 and 116, respectively. The clamping blocks 114 and 116 are screwed into the upper flange 70 of the objective lens spool 72. Opposed arms 118 and 120 of the leaf springs 110 and 112, respectively, are biased outwardly against their associated drive mechanisms 108 and 109. The other opposed arms 122 and 124 of the leaf springs 110 and 112, respectively, are biased inwardly toward the disc 92. Inserts 126 of hard material, such as sapphire, are inserted into openings in the arms 118, 120, 122 and 124 of the leaf springs 110 and 112 Where these leaf springs contact the drive mechanisms 108 and 109 and/or the disc 92.

The contact between the arm 118 of the spring 110 and both arms 120 and 124 of the spring 112 and the disc 92 are similar and are shown in FIGS. 4 and 5. These con- 6 tacts include balls 128 held in cup-like retainers 130 which are inserted into blind holes in the rim of the disc 92 (see FIG. 5). The balls 128 bear upon the sapphire inserts 126.

The contact between the disc 92 and the arm 122 is made by means of a Wedge 132 which fits into a V-shaped notch 134 in the insert 126 on the arm 122. Only the insert 126 of the arm 122 has such a notch. This wedge 132 provides a pivot for the disc 92 about which it may be rotated by the drive mechanism 108. All of the contacts, that is, the balls 128 and the wedge 132, are n the same plane.

One of the drive mechanisms is best shown in FIG. 5. Both mechanisms 108 and 109 are substantially identical. They include cylindrical sleeves 136 which pass through openings in the upper flange 70 of the lens spool. These lens spool openings are aligned with openings 138 in the housing 10. A portion of the sleeve 136 is internally threaded. The inner end of the sleeve is closed except for a center hole.

A shaft 144 extends radially through the opening 138 in the housing 10 and through the sleeve 136. A push rod 146 on the inner end of the shaft 144 extends through the opening in the inner closed end of the sleeve 136 'and bears against the sapphire insert 126 on the arm 120 of the leaf spring 112. An O-ring around the rod 146 is held in place by a packing gland nut 142, and provides a vacuum seal. The push rod adjoins an externally threaded shaft portion 148 which screws into the sleeve 136. A boss 150 forms part of the shaft 144 beyond the threaded part 148 thereof. The free end of the shaft extends through the opening 138 in the column 10. Gearing for accurately turning the shaft 144 for minute movements may be fastened to the free end of the shaft 144 by means of a screw 152.

Since the arms 120 and 118 of the leaf springs 112 and 110, respectively, are biased against the plungers 146 of their related shafts 144, any backlash in the screw threads of the threaded portion 148 thereof is prevented by the arms 118 and 120. The force for biasing the disc toward the push rods 146 of the drive mechanisms 108- and 109 is provided by the arms 122 and 124 of the respective springs 110 and 112. The arms 122 and 124 also provide biasing forces which add to the biasing forces of the arms 118 and 120 to further prevent backlash in the screw threads of the drive mechanisms 108 and 109.

When the shaft 144 of the mechanism 109 is turned, the disc 92 executes a rectilinear motion in directions shown by the straight line arrows 154 (FIG. 4). When the shaft of the other drive mechanism 108 is turned, the disc 92 pivots about the wedge 132 and executes arcuate motion in directions shown by the other, curved line arrow 156. Only rectilinear motion is possible in response to the drive mechanism 109, since the axis of its push rod 146 is perpendicular to a diameter of the disc 92 drawn between the balls 128 on the arms 124 and 118. These spring arms 118 and 124 therefore prevent any rotational movement of the disc 92. On the other hand, the pivot point provided by the wedge 132 permits rotational movement of the disc 92. Thus, by adjusting the position of the shafts 144 of both the drive mechanisms 108 and 109, different, desired orientations of the disc 92 and, consequently, of the specimen mounted therein may be obtained.

The axes of the shafts 144 of both drive mechanisms 108 and 109 and the points of contact between the disc 92 and the springs 110 and 112 are all in substantially the same plane perpendicular to the electron beam axis. Accordingly, no tilting or other inclination of the disc 92 with respect to the axis of the column 10 and with respect to the electron beam axis occurs when the drive mechanisms 108 and 109 are adjusted. A specimen carried by the disc 92 therefore is always maintained in the same transverse plane with respect to the electron beam axis of the column. Thus, false stereoscopic images of the specimen will not result.

Specimen refrgemtz'ng singe in general An adapter 158 (seeMFIG. 3) is receivedwithin the conically tapered Vopening 94 in the disc 92. This adaptor 158 is madeyof a suitable insulating materiahsuch as alumina ceramic. The adaptor 158 is generallyof hollow conical shape. Part of its outer periphery has a taper which is conjugate to the taper of rthe opening 94 in the disc 92. The lower end of the adaptorextends well within the upperpole piece 8-2 so as to provide a thermal shield which surrounds the specimen holder, as will be more apparent as the description proceeds. The inner periphery of the adaptor 158 is formed with ya shoulder 160 adjoining a generally cylindrical internal wall 162. The shoulder 160 is precisely located with respect to the tapered, outer periphery of the adaptor. Thek shoulder 160 provides a reference position for the specimen mounting, the use of which is explained hereinafter. y Y

The adaptor 158 is desirably metallized on all of its external surfaces except the shoulder 160 and the internal cylindrical wall 162. A metal Vsuch as silver may4 be evaporated on the desired surfaces of the adaptor. This provides a metallic coating which carries away any charges which might otherwise beV accumulated o nzthe surfaces of insulating material forming the adaptor 158.

The refrigeration equipment of the specimen stage may be considered in twovparts. One of these parts 164 provides for mounting the specimen in precise location on the adaptor 158, and is referred to herein as the specimen mounting part., The other of these parts 166 is associated with the refrigerant which absorbs the heat from thel specimen and cools the specimen to the desired, low temperature, and Vis referred to herein as the refrigerant part 166. A removable drum-like case 168 carries or contains these parts 164 and 166 of the refrigerated specimen stage. The disposition of the case 168 within the stage 30is discus'sed in greater detail hereinafter. Many of the refrigerated stage parts may be removed merely by withdrawing the case 168 from the columnthroughrthedoor 13 (FIG. 2) therein. After the case 168 is removed, the adaptor ring V 158 (FIG. 3*) may also be removed. lThe adaptor ring lmay, however, be secured to the specimen mounting part 164 and form a unitary structure therewith, whereby the adaptor is removed with the case,168,w The disc 92Vmaykthen receive aconventional specimen holder in its opening 94.

Specimen stage specimen mounting part The specimen mounting part 164 includesy a collar 172 'which is a generally cylindrical tube having anrinternal wall of cylindrical form at its lower end and conical forrn at its upper end. A specimen holder 174 is received withf in the collar 172. The specimen holder has an outer wall conjugate to the internal wall of thecollar 172 sorasto fit into the collar 172. The specimen holder 174 also has a an'ge 176. j t Y Y The upper end of the collar 172 is of greate'rrdiamet'er than the lower end thereof. The lower part of the collar is tapered inwardly from an externally threaded portion 182. The threads are intended to 4receivey a threaded ring 184 through which the lower part of the collar 172 passes. This ring 184 serves to position the specimen mounting on the shoulder 160( of the adaptor 158. The ring 184 has a cylindrical outer periphery and a dished, conical, upper surface. i v t The heat exchanger 64 (FIG. 1) includes, in part, a plurality of disc-like heat exchangerwns 186 secured to the collar 172 with they ring 184. Each iin includes an outer, circular, flange portion 188,*a conical center portion 190, and a short, circular, inner flange 192 which extends from the conical center portion. The fins 186 are assembled in stacked relationship on the collar 172 by means of spacer rings 194 which, with the internal flanges 192,l are clamped together between the bottom of the larger diameter, upperV end of the collar 172 and the dished surface of the threaded ring 184. Each fin 186 is thick enough to be rigid and self-supporting. Therefore, the fins 186 canbe mounted (as shown) along their inner flanges as cantilevers. The fins are made of conductive material. j Chemically blackened brass is preferred. The fins are dimensioned with their thickness related to their Yradius 'so that good heat exchange is obtainedy therefrom. y l

summarizing, the yspecimen mounting part 164 includes the collar 172 on which the fins 186 are mounted by means of the ring 184. The ring 184 is received within the cylindricai, internal wall 162'o'f the adaptor 158 and is precisely located by means ofthe shoulder on theadaptor 158. The specimen holder 174 is received in precise positional relationship in the opening through the collar 172 since its conical, external wall snugly embraces the internal wall of the collar 172 in exact position therein, the elevation of the holder being set by the external taper on the specimen holder 174 land the internal taper on the upper part of the internal wall of the collar 172.

The specimen is secured vin the specimen holder 174 at the lower end thereof, immediately above the upper polev piece ,86, by means of a cap 196l which is threaded onthe lower end of the holder 174. The specimen holder 174 will be described in greater retail in connection with FIG. 6 of the drawings. Y

Specimen stage refrigerant part The refrigerant part 166 includes the means for introducing and A storing the liquid refrigerant in the specimen stage 3i). Storage for the liquidrefrigerant is provided by a hollow lreservoir or receptacle 212 which forms a toroidal channel 212e.` The receptacle 212 has a conically tapered, outer, peripheral -Wall and a cylindrical, inner, peripheral wall. A yiiange 213 extends outwardly from the lower edge of the outer, peripheral4 wall.u Sectors are cut out of this ange to provide clearance for other parts.

A pair of ears 216 (only one appears in FIG. 3, both being shown in FIG. 2) are securedto the upper Wall of the receptacle 212 as by bra'zing, for example. These ears 216 have holesy therethrough which provide entry into the liquidrefrigerant channel of the receptacle 212. Pipe nipplesll/S (FIG. 3) are inserted into the ears 216 'and fastened thereto by brazing. Flexible pipes 220,y

which maybe made of corrugated,.svtainless steel, are brazed tothe nipples 218. These pipes 2,20 are connected to hereinafter described entry ports 222 for the liquid refrigerant. n Y e The previously mentioned curved baille plate 214 (FIGS. 2 and 3) of conductive materiahsuch as brass, is secured, as by brazin'g, ona shelf 215 which extends outwardly from the upper wall of theV receptacle 212. v

As mentionedabove, asuitable liquid refrigerant is liquid nitrogen.l The liquid ynitrogen chills the receptacle and alsothe' balileplate 214. Thev peripheral surfaces of the receptacle 2112 and the baffle ppl-ate 214 are thus maintainedy very cold (for example, about These surfaces therefore act as ya cold trap on which any gasesk or kvapors present in the column may condense. rWhen such gases(A or vapors condense, ,the pressure in thecolumn is lowered and the Vacuum is made more perfect. v The greatest degree of condensing occurs Vat the cold baffle plate 214, since it is adjacent to a vacuum port 226 into Vwhich the vapors are drawn. Accordingly, vacuum pumping action is obtained through the use of the refrigeration apparatus., The condensed vapors may be readily removed fromvthe surfaces of the bafe 214 and of the receptacle 212 .by wiping V'the surfaces thereof. Access to the barile 214 and the receptacle 212 may be had through the rear door 19 in the housing part 11 (FIG. 2).

Two ports 222 are provided in the housing 10. The liquid nitrogen may be passed through these ports 222, the pipes 220, and ears 216 into the receptacle 212 without disturbing the vacuum and `Vwithout appreciable loss of liquid nitrogen by absorption of heat after initial cooling. One of the ports 222 for the liquid nitrogen may share the same bracket 224 as the vacuum port 226, or a separate vacuum port on the back of the housing may be provided. The vacuum port 226 is connected to the vacuum system 14 (FIG. 1) for the purpose of evacuating the column.

Each of the ports 222 for the liquid nitrogen includes a pipe 228 which has an outer wall 230 and an inner wall 232. The walls 230 and 232 are interconnected at one end thereof but are spaced from each other elsewhere. This folded-over pipe 228 .arrangement provides a long, thermal conduction path between the inner wall 232 of the pipe, which contacts the liquid nitrogen, and the outer wall 230 thereof which is connected to the housing 10. The thermal drop between the inner and outer pipe portions 232 and 230, respectively, is sufficient so that the column 10 does not serve as a major heat sink. Accordingly, the housing 10 does not contribute a significant amount of heat to the entering liquid nitrogen.

A clamping ring 234 which is secured to the bracket 224 by means of screws 236 encloses a gasket vacuum seal in the form of an O-ring 238. This ring 238 provides a vacuum tight connection between the column 10 and the pipe 228.

The vacuum port 226 includes a pipe 240 which is secured between the bracket 224 and the housing 10 in vacuum tight relationship by means of another O-ring 242. The pipe 240 is in engagement with a locking nut 244 which holds the pipe in place. A flexible hose 246 connects the pipe 240 to the vacuum system.

Both liquid nitrogen admitting pipes 220 are connected by means of ports similar to the port 222 to the exterior of the housing 10. Liquid nitrogen may be pumped into the reservoir 212 through either or both of the pipes 220 by connecting a hose from tanks of liquid nitrogen to the pipe 228. Alternatively, the liquid nitrogen may be poured into one of the pipes 228. The nitrogen vapors can be allowed to escape through the other pipe.

Under some circumstances, it may be desirable to llow the liquid nitrogen into one of the ports 222, through the reservoir 212, and out of the other of the ports 222. On the other hand, it may be desirable to use one of the ports 222 as a vent for vapors from the liquid nitrogen and to allow liquid nitrogen to enter through only one of the ports 222 to replace any nitrogen in the reservoir 212 which has evaporated.

The receptacle 212 is mounted on the upper flange 70 of the lens spool 72 (FIG. 3). The receptacle mounting is provided by at least three cylindrical pins 250 of insulating material, such as nylon. Unly one of the pins 250 is shown in FIG. 3. The pins 250 have reduced diameter ends which extend into openings in the flange 213 on the receptacle 212. The pins 250 are disposed in blind holes 252 in the upper flange 70 of the objective lens spool 72. The pins are spring biased upwardly by compression springs 254. Since the pins 250 are of insulating material, the receptacle 212 is out of thermal contact with the microscope housing 10 and the column and does not gain heat rapidly from the housing 10 or from the column. The spring biased pins 250 also allow some vertical movement of the entire refrigerant part 166 of the stage 30.

In order to provide for vertical translation of the part 166, there is provided a cylindrical ring 256 (FIGS. 2 and 3) of insulating material, such as nylon. The lower edge of the ring 256 has three tab-like, downward projections 259 which engage the flange 213. The use of three points of contact between the receptacle and the ring 256 further reduces thermal losses. A cylindrical flange 258 extends radially beyond the outer periphery of the ring 256. A metal ring 260 of triangular cross-section is inserted between the outer wall of the ring 256 and its 10 flange 258 so as to provide a beveled edge on the ring 256 assembly,

The ring 256, and consequently the entire refrigerant part 166 of the refrigeration apparatus in the stage 30, can be moved vertically by means of two plunger mechanisms 261 and 263. These mechanisms include two rods 262 diametrically opposite each other. Each rod 262 has a tapered nose 264 which engages the beveled edge of the ring 260. The rear end of each rod 262 has a screw thread which is rotatable within a collar 268 by means of a knob 266 external to the housing 10. The collar is screwed into a threaded hole in the housing 10 and confines a vacuum seal by means of an O-ring 270 between the column, the rod 262 and the collar 268 to thereby prevent the loss of vacuum from the column through the threading in which rods 262 are rotated or inserted.

The case 168 is removably mounted on and within the inner periphery of the receptacle 212. A flange 217 extends from the upper wall of the case 168 and rests on the upper wall of the receptacle 212. This flange 217 has sections cut away to provide clearance for the ears 216.

The heat exchanger 64 is contained within the case 168 and the specimen holder 174 extends through a hole 170 in the center of the upper wall of the case. The heat exchanger 64 includes a plurality of fins 198, which are mounted on the internal cylindrical side wall of the case 168. The fins 198, like the fins 186, are funnel-like in shape and each includes a circular llange 200 from which a frusto-conical part 202 extends in an inward and downward direction. The fins 198 are preferably made of sheets of chemically blackened brass and have thickness and radial extent related for optimum heat exchange effect according to known fin design practice. The hns are sufficiently thick to be rigid and self-supporting when mounted along their rims as cantilevers. The fins 198 are assembled in stacked relationship between a circular, flat shoulder 204 which extends horizontally from the inside of the side wall of the case 168 and a disc 208. The fins 198 are separated from each other by means of spacer rings 206 which engage the outer marginal portions of the anges 200. The circular disc 208 is screwed into the bottom of the side wall of the case 168 and forms the lower end wall thereof. The disc 208 clamps the fins 198 and the spacer rings 206 between the shoulder 204 and the upper surface of the disc 208 which also acts as a radiation shield. The assembly of the hns 198 on the case 168 and the ns 186 on the collar 172 is accomplished conjointly so that the fins 198 are interleaved with the fins 186.

A heater 278 is mounted on the upper end wall of the case 168 for the purpose of allowing the establishment of temperatures between the ambient and liquid nitrogen temperatures in the vicinity of the specimen. This heater 278 is mounted in a removable cap 280 which is centrally apertured for the passage of the electron beam. The removable cap rests in thermal Contact with the case 168 and therefore with the reservoir 212. Accordingly, some heat may be given by the heater 278 to the receptacle 212 and to the case 168 so as to cause the temperature of the fins 198 to be held stable at intermediate temperatures within the range from liquid nitrogen temperature to the ambient temperature. Heating is accomplished by a non-inductive wafer type heater 282 of known design which is parallel to the disc 92 and therefore with the flange portions 200 and 188 of the tins 198 and 186, respectively. Since the heater 282 is non-inductive, it does not interfere with the electron beam or the electron optics of the system.

The refrigerant part 166 of the stage 30 and the specimen mounting part 164 thereof are mechanically independent of each other because they have independent means of support which position these stage parts 164 and 166 so as to be separate from each other. This me- ,chanical independence results from the dimensions, position and shapes of the parts themselves Vand their mountings. The specimen mounting part 164 position is refer enced by the shoulder 160 of the adaptor 153. The refrigerant part 166 is positioned by the insulating pins 259. The insulating pins and the shoulder 160 are so related inrelative height that the specimen ymounting part 164 oats free of the refrigerant part 166. The parts may, however, be brought in contact with each other if desired by vertically moving the refrigerant part by means of the two rods 262.

The specimen holder 174 also floats free of the refrigerant part 166. When the holder 174 is received within the collar 172, it is positioned with its flange 176 separated from the upper end Wall of the case 16S by a small clearance 178. This clearance results from the t of the conical section of the holder 174 and the conical section of the interior wall of the collar 172 which sets the position of the ange with respect to the reference shoulder 160 of the adaptor 158.

In summary, the construction of the refrigerantV part 166 of the apparatus includes the case 168 on which the heat exchanger fins 198 are mounted in cantilever fashion interleaved in concentric relationship with the fins 186 of the specimen part 164. The receptacle 212 receives a liquid refrigerant, such as liquid nitrogen, and provides a seat for the case 168. The case 168 and its associated parts are also mounted in heat insulating relationship with the objective lens spool 72 and may be moved in a vertical direction by means of the insulating ring 256 and the knob controlled plungers 262. A heater 282 in heat exchange relationship with the receptacle 212'through the case 168 makes the temperature in the stage controllable from ambient to liquid nitrogen temperatures.

Specimen stage operation Two modes of cooling are provided for in the specimen stage 30. These are cooling by radiation and cooling by conduction. Cooling by conduction is especially vdesirable when the specimen is to be refrigerated rapidly. They refrigerated condition is then desirably maintained by continuing the cooling by radiation.

`In order to cool by conduction, the .knobs 266. are turned to withdraw the rods 262 outwardly and away from the ring 256. `The case 168 then rises under the bias from the springs 254 until the upper end wall of the case 168 contacts the flange 176 `of the specimen holder 174. A direct thermal conduction path is therefore obtained betained between the specimen held bythe cap 196 at the lower end of the holder 174 and the receptacle 212.

When cooling by radiation is desired, the rods 262 are advanced inwardly to cause the ring 256 to move downwardly. The entire receptacle 212 and case 168 then move downwardly with the spring biased plugs 250until the clearanceA 178 is again established between the flange 176 on the specimen holder 174 and ythe upper end wall of the case1'68. `The case 168 andthe ns 19,8 of the refrigerant part 166 also oat free of the fins 186 of the specimen mounting part'164. Coolingthen proceeds by radiation between the fins. the lins, even by radiation, is efficient because of the thermo-mechanical relationships of the interleaved fins 198 and 186. When the cooling is by radiation, the specimen mounting part 164 is completely, free of the refrigerating part 166. refrigerating part 166, such as would be caused by percolation of the liquid nitrogen in the receptacle 212, are not transferred to the specimen holder. Accordingly, unwanted excursions, vibrations orother movements of the specimen due to movements of the refrigerant part 710 166 are prevented. n

Thermally induced movements of the specimen are also small because of the bi-part construction of the stage 30. The parts of the stage 30 may be made smaller than in the case where a large, integral structure would be used. i

The Vheatexchange between Thus, any movements of the 'j' 12 f Movements of such small parts due to thermal expansion and contraction are reduced 'correspondingly with theirsmall size and have been found to have a negligible effect on the operation of the stage and the use thereof in electronrnicroscopy. p

The heavier part of the refrigeration apparatus is the refrigerant part 166. The refrigerant part 166 is not mechanically coupled to the movable disc 92. Only the specimen mounting part 164 moves with the disc 92. This feature of construction reduces the mechanical loading on the drive mechanisms for the disc 92 and makes orientataion of the disc 92 much more readily and easily accomplished.

The concentric, coaxial relationship of the ns in the heat exchanger 64, the refrigerant receptacle 212 and most of the other parts associated with the refrigeration apparatus also alleviates adverse affects on the electron optics of the system. The electrical and magnetic fields established in the vicinity of the electron beam which might Vbend or tilt the beam have a negligible effect because of the concentric, coaxial relationship of the tins and other parts of the apparatus.

Specimen holder The specimen holder A174 is 'shown in greater detail in FIGS. 6 and 7. The holder is providedby an open-ended, tubular structure 290 which has the flange 176 extending from its upper end. This structure is desirably of copper. The lower reduced end of the tubular structure is formed externally with threads 292. The cap 196 is threaded internally, andhas an aperture 294 coaxial with the tubular structure 290. The cap 196 isscrewed onto the threads 29,2 and firmly holds a specimen ,296 across the bottom .of the tubular structure 290. The tubular ystructure 290 has a conically tapered section 298 which is received within the opening inthe collar 172 (FIG. 3). Otherwise, the structure 290is cylindrical in shape. The lower section of the tubular structure 290 has cylindrically shaped interior wall. The bottom part 293 of this lower interior Wall is reduced in diameter from the remainder thereof 'so as to engage the lower end of an open-ended, frusto-conical tube 300 therewithin.

j A thermocouple junction 302 is formed where the tube 300 and lstructure 290 engage each other. This junction is cylindrical in shape and contacts the specimen 296. The tube 300 does not touch the tubular structure 290 except at the junction 302. The tube 300 is desirably made of stainless steel. A columbium or titanium stabilized stainless steel having a carbon content of less than 0.02% is preferred, since such a stainless steel is especially suitable for silver brazing. A suitable stainless steel is described in the Stainless Steel Handbook, published by Allegheny-Ludlum Steel Corp., Pittsburgh, Pa. (1956) as Type3l6 (see page 3 of the referenced handbook).

The thermocouple junction may be formed by silver brazing the tube 30.0 to the copper tubular structure 290.

A flanged, hollow cylinder 304 of copper provides one electrode of the thermocouple. This cylinder is disposed in. telescoping relationship with the tubular structure 290 at the top thereof Vand is held in place by means of a clamping spring 306 (FIG. 7). A circular part 308 of the spring 306 surrounds theV outside of the tubular structure 290. A straight part 310 of lthe spring 366 extends through a slot 312 in the tubular structure 290 into engagement with the flanged, hollow cylinder 304 at a notch 314 therein.

A grommet 316 of insulating material, desirably a vceramlc, 1s mounted inside the hollow cylinder between a lip` 318 and an internalb cylindrical shoulder 320 thereof. A hollow, stainless steel cylinder 322 which has a tapered end portion 324 of enlarged diameter extends through the opening in the grommet 316 with the tapered portion securely disposed VWithin the stainless steel tube 300 at the upper end thereof. A stainless steel spring 326 around the outsideof the tube 322 serves an a confactor. A stainless steel lead 328 may be connected to the spring 326. A copper wire 330 may be connected to the copper cylinder 304. These wires 328 and 330 provide electrical connections to the junction 302. Vacuum tight feed-through grommets (not shown) are provided in the wall of the housing 10. The leads 328 and 330 are brought out of the housing through these grommets.

The electron beam passes through the hollow cylinder' 322, the stainless steel tube 300, the specimen 296 and the aperture 294 in the cap 196. The concentric, coaxial construction of the thermocouple specimen holder is especially suitable for electron optical systems since all parts of the holder are symmetrical with respect to the beam and do not exert any inlluence on the beam or the electron optics of the microscope. The choice of copper for the outer, tubular structure also provides a high conductive path between the fins 186 on the specimen mounting and the specimen so as to facilitate rapid cooling thereof (sce FIG. 3). The symmetrical geometry of the holder also provides for uniform cooling of the specimen 296. The specimen holder 174 may be removed by means of a plier-like tool which engages the flange 176 thereof. The tool may also be used to remove the case 168 including the heat exchanger and specimen mounting part 164.

It has been found that a thermocouple junction such as described above has a substantially linear response characteristic over the temperature range from ambient temperature to liquid nitrogen temperatures in that the output voltage from the thermocouple changes substantially linearly with changes in temperature over the operating range of the refrigeration apparatus. Since the copper and stainless steel parts are spaced from each other except at the junction, there are no hidden junctions or short circuits in the electrical circuit to the junction 302.

An electrical circuit suitable for operating the thermocouple is shown in FIG. 8. The junction 302 in the vicinity of the specimen is connected in series with the junction 330 which may act as a reference junction by being coupled to an ice water bath so as to maintain its temperature at zero degrees centigrade. The reference junction 330 and the thermocouple junction 302 in the holder 174 are connected in series opposing relationship (the junction 302 and the junction 304 are oppositely polarized). The net voltage difference between the output of the reference junction and the junction 302 is applied to an amplifier 332 which may be a D.C. amplifier of the chopper type. The output of this amplifier is a D.C. voltage which may be measured on a sensitive meter 334. Since the thermocouple 302 in the holder 178 has a linear response characteristic, the scale of the meter may have a linearly calibrated temperature scale, which linearity facilitates reading temperatures from the meter.

What is claimed is:

l. In a scientific instrument, apparatus for controlling the temperature environment of a specimen comprising (a) means for establishing a temperature therein different from the ambient temperature,

(b) means for mounting said specimen spaced from said temperature establishing means, and

(c) relatively movable means coupled to said temperature establishing means and to said mounting means for selectively providing heat exchange by one or the other of conduction and radiation between said temperature establishing means and said mounting means. Y 2. A scientific instrument as set forth in claim l comprising an electron microscope having an evacuable housing along an axis of which an electron beam is adapted to travel, and wherein said means for mounting said specimen forms part of a specimen stage comprising (a) a plate disposed transversely with respect to said axis and having a central opening therein for receiving a specimen holder,

(b) a support member disposed in said housing adjacent to one face of said plate,

(c) a plurality of ball bearings disposed between said plate and said support member movably mounting said plate for movement in all directions in its own plane,

(d) a plurality of spring members extending inwardly from said housing over the face of said plate opposite said one face,

(e) other ball bearings separately disposed between said opposite face and said spring members, and

(f) means for orienting said plate in any of said directions in its said plane, said means including movable members engageable with the edges of said plate at diametrically opposed points all in the same plane.

3. A scientific instrument as set forth in claim 1 comprising an electron microscope having an evacuable casing and an objective lens in said casing including a anged lens spool around which an energizing coil is wound, and wherein said means for mounting said specimen forms part of a specimen stage for said microscope comprising (a) a plate for carrying specimen holder movably mounted on a ilange of said objective lens spool,

(b) a pair of ball bearings mounted diametrically opposed to each other on the edge of said plate,

(c) a wedge mounted on said edge of said plate,

(d) another bearing mounted on said edge diametrically opposed to said wedge,

(e) said bearings and said wedge all being in the same plane,

(f) means for translating said plate engageable with the one of said bearings which is diametrically opposite to said wedge, and

(g) means engageable with one of said pair of iirst named bearings for rotatably moving said plate about said wedge as a pivot.

4. A scientific instrument as set forth in claim l cornprising an electron microscope having an evacuable casing and an objective lens in said casing including a flanged lens spool around which an energizing coil is wound, and wherein said means for mounting said specimen forms part of a specimen stage said microscope comprising (a) a plate carrying a specimen holder having one face thereof adjacent to one flange of said objective lens spool,

(b) ball bearings disposed between said flange and said one face of said plate for movably mounting said plate on said flange,

(c) hold-down springs disposed adjacent to the opposite face of said plate,

(d) a plurality of ball bearings each biased by a different one of said springs against said opposite face of said plate,

(e) a pair of ball bearings mounted in diametrically opposed relation to each other on the edge of said plate,

(f) a wedge carried on said edge of said plate,

(g) another ball bearing mounted on said edge diametrically opposite to said wedge,

(h) leaf springs on said casing biased against said wedge and one of said pair of diametrically opposed ball bearings,

(i) means for rectilinearly translating said plate including a rod movable radially of said casing for applying force against the one of said bearings which is diametrically opposite to said wedge, and

(j) means for rotatably moving said plate about said wedge as a pivot including another rod movable radially of said casing for applying force against the (d) means providingrelative .movement of 4said temperature establishing means and saidinounting means for selectively establishing .in SaidQhe'at exchange means radiative .and conductive heat .exchange between said mounting means and said temperature establishing means.

6. Apparatus for use in a scientific instrument for refrigerating a .specimen undergoing examination, said apparatus comprising t (a) a mount .frcrryng a specimen, Y

(h) at refrigeratry body airound said mount and spaced therefrom, and Y, Y v (c) relaitvelyY movable meanscoupled to. said mount and to said refrigeratory body for selectively coupling said bodyandsaid mount in one 'or another 'of a irst heat exchange relationship lwhereingheat is exchanged. therebetween by tlerr'nal'v conduction and a second heat exchanger relationship wherein Y heat is` exchanged therebetween by thermal radiation, 7. Ina scientific, instrument apparatus for refrigerating a specimen, said apparatus comprising (a) a specimen mount, ,Y Y f '(b) a refrigeratory body spaced from said mount, (c2 meansrfr siipprti'rig'. said Vmount and said body in said instrument in insulating relationship with each other, ,A Y (d) a plurality of heat-exchange elements mounted separatelyl onl said body and on said inounvand (e) means for moving said refrigeratory` lbody with respect to said mount to bringr said elementsinto and out of cntactwitheach other whereby toalternatively provide ,heat excliang'e'fbyz radiation"y and by f condction between said body and saidV mount` 8. Apparatusfor re'frigeratinga specimenuadapted to be examined in a scientific instrument, said apparatus Comprising l (a) a mount for receiving said' specimen; (b) anannula'rtrefigeratory bodyarnnd said-mount, (c) a iirst plurality of rigid heat exchange tins extending inwardly Afrom said bodytoward said mount, (d) a second plurality'f heat exchange ytins extending outwardly from said mount toward said body and interleaved with said first' pluralityof ns and Y (e) means for moving saidv body- `for` selectively providing heat exchange by radiation and by conductive contact between said body iins and said mount tins. 9. A specimen stage for a'n electron microscope, said stage comprising (a) an annular refrigeratory body,

(b) aplurality of annular: iins extending inwardlyv from said body, i w l (c) an annular, mount' for; receiving a specimen disposedcoaxially with saidlbuody,

(d) said. mount having .a plurality of annular tins extending outwardly therefrom towards said refrigeratory body and interleaved with said fins extending from said body,

(e) an insulating support on which said mount is disposed, f

(f) an insulating support yieldably mounting said body for movement in an axial direction, and

(g). means for moving said `body in its said yieldable mounting to provide heat exchange selectively by conduction and by radiation between said body tins and said specimen mount tins.

10. In an electron microscope having an evacuable housing through which an electron beam is projected and including an electron optical system having an objective lens, a specimen stage which comprises (a) a movable plate having anopening for the passage oi' said beam, said plate being mounted on an end of said objlective lens,

(b) a ringof insulating material in said opening,

(c) a tubular, .cylindrical collar mounted in said ring, said collar being adapted to receive a cylindrical specimen holder therein,

(d) a hollow ring for containing a liquid refrigerant disposed around said collar,

(e) a plurality of members of insulating material slidably mounted in rsaid housing on said objective lens and springbiasedinto supporting engagement with said refrigerant fring, 1

(f) a plurality of rigid, disc-like tins extending outwardly from said collar and inwardly from said ring in interleaving relationship with each other to provide heat exchange therebetween,v f

(g) an insulating ring around saidvrefrigerant ring engaging saidy retrigerantrng along one of two oppositeend edges of said insulating ring, the other of said Ytwo ended ges being tapered,

(h) a rod extending ,through said housing, said rod having a tapered nose in engagement with said tapered edge of said insulating ring, and Y (i) Vmeans for` moving saidVv rod inwardlyandoutwardly with respect to said casing. for moving said insulating ring in -the direction of the path of said beam @thereby nwrgsaiciv refrigerant riss .in Said. direction,v the movement of 4said Vretri gerant lrin g selective ly providing heat exchange by conduction and by radiation between said-tins. 5 n w (11..y Inman kelectron microscopevhaving an evacuable housing and means for projecting an electronA beam along the axis of saidhousinga specimen stage forvmo'unting a specimen in the path of said beam, said stage comprismg. (a) a refrigeratorytbody meente/d in insulating relationship with said housing and coaxially therewith, said refrigeratory body comprising l (l) an annular member having a toroidal channel for a liquid refrigerant, (2) a baille. Vounted onV said annularmember, (3) said annular member having atleast one opening therein comrntnic'ating with said channel for introducing said liquid refrigerant into said 'channehsaid bathe providing a cold-trap insaid housilg,

(b) an'v annular mounting for a specimen lolder disposed within said body and mounted in insulating relationship within said housing, and

(c) heat `exchange means includinga plurality onannular, interleaved ins mounted separately on said annular member and on said body.

l2. In an electron microscope having an evacuable housingalong the axis of which' an 'electron ,beam passes from a source to a target, a specimen retrigerating stage which comprises (a) a hollow, annular body having a tor'oidal channel therein, K u

(b) a hollow, cylindrical case having a central opening therethrough, said case being mounted on and within said body,

(c) means for introducing a liquid refrigerant into said channel,

(d) a plurality of spring biased insulating elements mounted in said housing and engageable with Said body for carrying'said body and said case,

(e) a plate mounted in lsaid housing and transversely movable with respect to said housing axis, said plate having an opening therein,

(f) a first ring of insulating material removably disposed in said opening.

(g) a tubular collar extending through said central opening in said case and mounted on said first nsulating ring,

(h) a iirst plurality of cantilever ns of disclike configuration mounted along their outer edges on the inner periphery of said case,

(i) a second plurality of cantilever tins of disc-like conguration mounted along the inner edge thereof on the outer Wall of said collar and disposed in interleaved relationship With said rst plurality of tins mounted on said case,

(j) a second ring of insulating material disposed around the outer periphery of said case and engageable with one of said case and said body along one edge of said second ring, the outer edge of said second ring having a bevel, and

(k) a pair of rods diametrically opposite each other and extending radially through said housing, said rods having tapered noses engageable with the beveled edge of said second ring for moving said second ring, said case and said first plurality of iins in a direction axially of said housing.

13. in an electron microscope having an evacuable housing along the axis of which an electron beam passes from a source to a target, a specimen refrigerating stage which comprises (a) a hollow, annular body having a toroidal channel therein,

(b) a hollow, cylindrical case having a central opening therethrough and having a peripheral flange extending outwardly therefrom and disposed on said body so that said case is positioned centrally within said body,

(c) means for introducing a liquid refrigerant into said channel,

(d) a peripheral flange extending outwardly from said body,

(e) a plurality of spring biased, insulating elements l mounted in said housing and engageable with said flange for carrying said body and said cylindrical case,

(f) a plate mounted in said housing and transversely movable with respect to said housing axis, said plate having an opening therein,

(g) a rst ring of insulating material removably disposed in said opening,

(Ii) a tubular collar extending through said central opening in said case and mounted on said lirst insulating ring,

(i) a rst plurality of cantilever fins of disc-like coniguration mounted along their outer edges on the inner periphery of said case,

(j) a second plurality of cantilever tins of disc-like configuration mounted along the inner edge thereof on the outer wall of said collar and disposed in interleaved relationship with said iirst plurality of ns,

(k) a second ring of insulating material disposed around the outer periphery of said body and engaging said body along one edge of said second ring, another outer edge of said second ring having a bevel, and

(l) a pair of rods extending radially through said housing and disposed diametrically opposite each other, said rods having tapered noses engageable with said bevel of said second ring for translating said second ring, said case and said tirst plurality of fins in a direction axially of said housing.

References Cited hy the Examiner UNITED STATES PATENTS 2,220,973 ll/ Marton 250-49-5 2,420,560 5/47 Ramo Z50-49.5 2,514,382 7/50 Freidman et al. Z50-51.5 2,543,825 3/51 Ben et al. 250-5l-5 2,728,840 12/55 Columbe Z50-51.5 2, 826,701 3/58 Colunibe 250-49.5

40 RALPH G. NILSON, Primary Examiner. 

1. IN A SCIENTIFIC INSTRUMENT, APPARATUS FOR CONTROLLING THE TEMPERATURE ENVIRONMENT OF A SPECIMEN COMPRISING (A) MEANS FOR ESTABLISHING A TEMPERATURE THEREIN DIFFERENT FROM THE AMBIENT TEMPERATURE, (B) MEANS FOR MOUNTING SAID SPECIMEN SPACED FROM SAID TEMPERATURE ESTABLISHING MEANS, AND (C) RELATIVELY MOVABLE MEANS COUPLED TO SAID TEMPERATURE ESTABLISHING MEANS AND TO SAID MOUNTING MEANS FOR SELECTIVELY PROVIDING HEAT EXCHANGE BY ONE OR THE OTHER OF CONDUCTION AND RADIATION BETWEEN SAID TEMPERATURE ESTABLISHING MEANS AND SAID MOUNTING MEANS. 